When producing an amino acid by a fermentation method, the amino acid which has accumulated in the culture is recovered usually as a solid. Examples of methods for the recovery as a solid include a method which comprises removing the microbial cells from the culture, passing the residue through a resin column or the like to remove impurities thereby preparing a crude solution, conducting condensation or the like to precipitate the amino acid as crystals, and then separating the crystals from the solution (hereinafter referred to as solid-liquid separation) to recover the amino acid as crystals.
However, crystals which are, for example, flaky or in a fine powder form have a poor suitability for solid-liquid separation and necessity of a prolonged crystal drying time due to the shape thereof, and there are cases where product quality and production cost are considerably affected. In addition, such crystals which are flaky or in a fine powder form have a low specific gravity and are bulky. Thus, not only the small amount of the crystals can be packed into containers having a certain capacity and this packing is not efficient from the standpoint of transportation, but also there is a possibility that the amount of the crystals usable in final products is limited.
Examples of methods for avoiding such demerits include a method in which the amino acid to be obtained is recovered as large crystals from a solution containing the amino acid. Patent document 1 discloses a technique in which when an amino acid of interest is crystallized out after addition of seed crystals of the amino acid, the size of the amino acid crystals which are to separate out can be controlled by adjusting the particle diameter and concentration of the seed crystals. Non-patent document 1 discloses the facts that the appearance of crystals of L-isoleucine is changed by addition of L-alanine and that granules of L-isoleucine are obtained, depending on the additive amount of the L-alanine.
However, neither of the two documents discloses or suggests a feature that L-valine granules can be acquired by adding L-glutamic acid to an aqueous solution containing L-valine.